1. Field of the Invention
This invention relates to a printing paste supply device for supplying a printing paste to an object, such as a squeegee apparatus or a screen printing machine by extruding the paste from a syringe which contains therein the paste, such as a solder paste prepared by mixing solder powder particles with a liquid with flux having a high viscosity, a conductive adhesive and the like.
2. Description of the Prior Arts
This type of printing paste supply devices which are arranged to extrude the printing paste contained in the syringe through a discharge opening thereof by applying to the paste an air pressure of the compressed which is introduced into the syringe or by means of a movable plate which is caused to move to push the paste moved by the pressure of compressed air are already known.
In a screen printing, a squeegee slides linearly on an upper surface of a screen in frictional contact therewith to force the paste through pattern apertures in the screen and on to an object to be printed. In order to ensure the uniformity of the quality or finished condition of printing as well as the accuracy of printing, etc., it requires to prevent change in viscosity of the printing paste at the time of performing each printing. In case where the printing paste is to be printed onto a printed circuit board by means of a screen printing machine, it must have a predetermined viscosity which is suitable for printing. This is particularly important since the miniaturization of printed circuit boards is accelerated day by day and accordingly a high density printing using a screen having minute pattern apertures therein is desired.
Among commercially available solder pastes for screen printing which are applicable to printed circuit boards, a solder paste which is produced by mixing solder powder particles of a low melting point having a composition of around 63% of Sn and around 37% of Pb and a liquid flux having a high viscosity and contains around 9.3% of flux is widely used. This type of commercially available solder paste is filled in a syringe-like container or a short cylindrical container made from synthetic resin.
The solder paste is a kind of material which has such a property that it has no fluidity when it is held in a stationary condition and obtains the fluidity when it is agitated, stirred up or vibrated that is, thixotropy. Accordingly, it is difficult to use the solder paste, as it is, after taking it out from the container, so that, in use, it is necessary to give the viscosity suitable for printing to the solder paste by agitating, stirring up or vibrating the solder paste. The known printing paste supply devices which extrude the past by merely making use of a pneumatic pressure, however, lack a function to sufficiently stir up and knead the paste and hence, additional steps or devices for sufficiently stirring up and kneading the paste become necessary before printing.
The present invention has been made in view of the above-mentioned drawbacks or disadvantages and it is a primary object of the present invention to provide a printing paste supply device which is constructed such that the printing paste contained in the syringe can be effectively and efficiently stirred up and kneaded and then is discharged from a discharge opening of the syringe while being given a viscosity suitable for the screen printing, and which is particularly useful for screen printing machines which are used in producing surface mount technology circuit boards suitable for use in high technology products.